Praying Mantis Ootheca
(Photo: courtesy of Chelsea Napier, Adelaide, South Australia)
This is not a cocoon of a caterpillar, but is the egg case of a Praying Mantis. It is a stiff foam-like object, sometimes angular or sometimes rounded, in size about 1 cm. It is usually attached to a branch or twig. Typically it contains about 100 eggs, which in due course hatch into baby praying mantids.
There are about 160 species of Praying Mantis in Australia, and each has its own habits and form of its egg-case.
(written 25 January 2017)